S.I.N. 72 Question - Angular Velocity?

Question: An Australian bushman hunts kangaroos with the following weapon, a heavy rock tied to one end of a light vine of length 2.0m. He holds the other end above his head, a point 2.0m above the ground level, and swings the rock in a horizontal circle. The cunning kangaroo has observed that the vine always breaks when the angle measure between the vine and the vertical reaches 60 degrees. At what minimum distance from the hunter can the kangaroo stand with no danger of a direct hit?

I used v=[tex]\sqrt{2gR(1-cos\theta)}[/tex] and got a velocity of 4.4
I don't know where to go from there.